1. Field of the Invention
The present device relates to an electric connector mounted on a printed circuit board, and in particular, to a surface-mount type electric connector.
2. Brief Description of Prior Developments
In general, an electric connector comprises a housing, and a plurality of terminals functioning as an electric contact, which are retained in the housing. In case of mounting the electric connector on a printed circuit board, a distal end portion of each terminal is accurately soldered onto a predetermined position on the printed circuit board.
In the case where a mating connector is attached to and detached from the connector mounted on the printed circuit board, generally, a stress is applied onto the soldered distal end portion (hereinafter, referred simply to as "solder tail") of the terminal on the mounted side. In particular, in the case where the mating connector is drawn out from the connector on a mount side, a considerably great stress is applied onto the solder tail. In order to reduce a stress applied to the solder tail in attaching and detaching the mating connector, the electric connector to be mounted on the printed circuit board is provided with, for example, a reinforcement member (hereinafter, referred simply to as "hold down member") for fixing the electric connector onto the printed circuit board, at its both side ends in the longitudinal direction. Specifically, the hold down member fixed on the printed circuit board receives a connector draw-out direction force so that an excessive stress is not applied onto the solder tail of the terminal. Conventionally, the aforesaid hold down member includes a type of holding down a connector from its lower side (mounting surface side), and a type of holding down a connector from its upper side (side opposite to the mounting surface side)(see U.S. Pat. No. 5,263,867).
An assembled connector is carried after being collectively received in a transportation tray with a predetermined number of articles. In this case, the tray is formed with a plurality of receiving grooves for each receiving the connector. In order to achieve tail protection for preventing a stress from applying to a solder tail of a terminal during transportation, the receiving groove is formed into a shape as shown in FIG. 6. Specifically, the bottom face of a receiving groove 100 is formed with a projecting portion 102 along the longitudinal direction thereof. The projecting portion 102 raises the housing of a connector 104 upward; therefore, a solder tail 105 and the bottom face of the groove 100 is prevented from contacting with each other so that a stress is not applied to the solder tail. Also, a width W1 of the receiving groove 100 is set larger than a width W2 of the connector 104 so that the solder tail 105 does not contact with side walls of the receiving groove 100. In particular, the surface-mount type connector 104 as shown in figure requires an accurate flatness of the solder tail 105. In this case, it is important that tail protection during transportation is achieved by forming the groove into the aforesaid shape.
In the process for manufacturing of the connector, first, a housing as molding product is carried to a predetermined supply stage by means of a transportation rail, and is fed from the supply stage to an assembly machine. And then, a plurality of terminals are driven into (pressed in) the housing by means of the assembly machine. In the final stage of the manufacture process, a hold down member is attached to both sides of the connector. At this time, the hold down member for holding the connector from its lower side (mounting surface side) is attached from the substantially same direction as an assembly direction of driving the terminals into the housing. Therefore, a head of the assembly machine is used in common with a process for driving the terminals and a process for attaching the hold down member, so that the machine can be, as a whole, simplified. However, this type of hold down member does not withstand against a force of drawing out the connector, as compared with the hold down member for holding down the connector from its upper side, that is, the hold down member disclosed in U.S. Pat. No. 5,263,867. On the other hand, the hold down member disclosed in U.S. Pat. No. 5,263,867 sufficiently withstands against the force of drawing out the connector. However, the hold down member is attached on a base extending from both sides in the longitudinal direction of the connector so as to be fitted from top;--for this reason, the hold down member projects from both sides of the connector. As a result, the hold down member occupies a relatively large space on a printed circuit board. Therefore, this causes a problem of lowering a mounting density of electric components on a printed circuit board.
Also, the hold down member disclosed in U.S. Pat. No. 5,263,867 is formed by bending a flat plate. Thus, the maximum mechanical strength depends upon a strength of a bent portion. Moreover, the hold down member has four bent portions; for this reason, a tolerance in each bent portion is accumulated, and there occurs a great error in a dimension of the finished hold down member. Therefore, there can not be obtained a preferable flatness in a portion of the hold down member to be soldered to the surface of the printed circuit board. In such a case, it is impossible to perform surface mounting of the connector in a preferable state even if the solder tail has an accurate flatness.
In an automatic mounting process of the connector, the connector is sucked up one by one from a transportation tray by means of a specific nozzle, and then, is carried onto the printed circuit board. Therefore, it is important that the connector is received in the receiving groove (see FIG. 6) of the tray T with directivity in some degree. In the case where the receiving groove 100 of the tray T is formed into a shape as shown in FIG. 6, however, the connector is shaky in the groove 100 during transportation, and a minimum directivity required for the connector is not obtained in the automatic mounting process. In particular, tail protection can be sufficiently achieved. Specifically, as shown in FIG. 6, the connector 104 is raised up by the projecting portion 102 of the receiving groove 100, and there is a clearance defined between the connector 104 and side walls of the receiving groove 100. If the connector 104 is placed in such a state, the connector 104 becomes unbalance and is shaky during transportation. For this reason, the solder tail 105 abuts against the side wall of the receiving groove 100; as a result, a stress is applied thereto.
It is considered as one means for solving the above problem that the tray side is provided with a projecting portion at a not-contact position with the solder tail, and the projecting portion is abutted against the housing of the connector so as to position the connector. However, if a demand for accuracy is made in the tray side in order to obtain a directivity of the connector required for the automatic mounting process and to achieve tail protection, the tray itself becomes expensive. In fact, in the automatic mounting process of the connector, the connector is taken out from the tray by means of the specific nozzle, and thereafter, the directivity of connector is corrected with precision by a camera monitor. Thus, when the connector is received in the tray, a directivity may be merely given to the connector in some degree. Therefore, high precision for the tray is not necessary. Taking the above circumstances into consideration, it is considered that the housing of the connector is provided with a projecting portion which abuts against the side wall of the receiving groove of the tray. However, if the housing is provided with such projecting portion, there is a need of widening a width of a transportation rail for supplying the housing to the assembly machine in a manufacture process of the connector in accordance with the projecting portion. Consequently, some measures must be taken against the connector manufacture machine side. Also, if the width of the transportation rail is widened, there is a possibility that the connector is shaky on the rail. Therefore, the connector can not be carried in a state of being tightly positioned, and protection of the solder tail having an accurate flatness can not be achieved.
It is accordingly the object of the present device to provide an electric connector which can perform a preferable surface mounting of a connector onto a printed circuit board with sufficiently hold down strength, and can enhance a mounting density on the printed circuit board. Further, it is another object of the present device to provide an electric connector which can improve tail protection during transportation without causing failure in a connector manufacture process and increasing a manufacture cost of a connector transportation tray.